Increasing Thiamine Concentrations in Lake Trout Eggs from Lakes Huron and Michigan Coincide with Low Alewife Abundance

Rainbow Trout Oncorhynchus mykiss were introduced to the Esopus Creek watershed in the Catskill Mountains of New York in the early 1880s. This introduction created a renowned naturalized fishery that remains important to the local economy today. The objective of this study was to determine whether the growth and condition of Rainbow Trout in the Ashokan Reservoir changed following the establishment of (1) Alewives Alosa pseudoharengus in the 1970s and (2) White Perch Morone americana in the 2000s by analyzing historical scale samples from 502 Rainbow Trout. The resulting data were used to compare length at age, von Bertalanffy growth curves, age‐specific annual growth increments, and relative weight before and after each introduction. Results indicated that growth of Rainbow Trout of ages <5 years generally increased following each introduction, while insufficient data for ages 5 and 6 made trends for older fish unclear. Rainbow Trout of ages ≤2 are believed to primarily use riverine habitats in this watershed, and therefore fish of ages >2 may best reflect reservoir growth. The mean relative weight of Rainbow Trout also increased between each period. The largest increases in both growth and condition were observed during the period after the introduction of White Perch, which was unexpected considering this species may have some diet overlap with Rainbow Trout and should be a poor forage species. Changes in watershed management and density‐dependent growth effects may explain these unexpected results. Our results, which largely suggest increased growth and condition over time, eliminate growth effects as a possible explanation for declining Rainbow Trout populations and suggest recruitment issues in the watershed require further investigation. This study contributes to our understanding of the interactions between introduced species and underscores the value of maintaining long‐term monitoring programs for assessing biological trends.

Section: Discussionmentioning

confidence: 95%

Changes in Growth of Rainbow Trout in a Catskill Mountain Reservoir Following Alewife and White Perch Introductions

George

Baldigo

Flaherty

et al. 2018

“…2003b; Riley et al. ), but the study of TDC in the Great Lakes is relatively recent and the mechanisms and relative importance of TDC as an impediment relative to Alewife predation on fry are debatable (see Krueger et al. ; Richter et al.…”

Section: Discussionmentioning

confidence: 99%

“…Regardless of the mechanism, reduced Alewife abundance and the emergence of Lake Trout wild recruitment are correlated temporally (Riley et al. ), and Lake Trout wild recruitment has increased substantially in Lake Huron since the Alewife population crashed there during 2002–2004 (Riley et al. ; He et al.…”

Section: Discussionmentioning

confidence: 99%

Factors Affecting Postrelease Survival of Coded‐Wire‐Tagged Lake Trout in Lake Michigan at Four Historical Spawning Locations

Kornis

Bronte

Holey

et al. 2019

Since the 1950s, fishery agencies on Lake Michigan have pursued Lake Trout Salvelinus namaycush rehabilitation through Sea Lamprey Petromyzon marinus control, harvest regulations, and stocking millions of fish annually. Stocking was prioritized at four historically important spawning locations beginning in 1985, and coded wire tags (CWTs) were used to help evaluate performance. We used data from coded‐wire‐tagged fish captured in fishery‐independent surveys from 1998 to 2014 to evaluate relative postrelease survival of Lake Trout, estimated by CPUE and corrected for the number of fish stocked, across 173 CWT lots of the 1994–2003 year‐classes stocked at the four locations. Boosted regression tree models were used to assess the relative influence of four variables on Lake Trout CPUE in two age‐groups (ages 4–5 and ages 6–10) and were paired with ANOVAs to test for statistical significance. Genetic strain (29.1%), stocking location (27.8%), mortality at release (23.1%), and predator density (19.9%) had similar influences on the relative survival of younger fish, whereas the relative survival of older fish was heavily influenced by stocking location (79.8%). Survival of both age‐groups was lowest for fish stocked in the Northern Refuge, where the age structure was truncated due to fishery harvest and Sea Lamprey predation. Survival of stocked fish was higher at the Southern Refuge, Clay Banks, and Julian's Reef, where mortality from Sea Lamprey and harvest was lower and where increases in wild Lake Trout have been observed in recent years. Stocked Lake Michigan remnant genetic strains also appeared to survive better than strains from other lakes at these three locations, but strain effects could not be fully disentangled from the effects of stocking location, and the continued stocking of multiple genetic strains may provide resiliency to future selection pressures. Continued progress toward rehabilitation will require reducing fishing and Sea Lamprey‐induced mortality in northern Lake Michigan to build parental stocks of advanced ages as well as balancing efforts among competing management goals.

“…This complex is linked to a maternal diet of Alewives Alosa pseudoharengus that causes a thiamine deficiency in eggs that result in poor hatching success and high posthatch mortality among fry (Fisher et al 1996). In Lake Michigan, mean egg thiamine levels in Lake Trout have increased in recent years and are correlated with a concomitant decrease in Alewife abundance (Riley et al 2011). Lake Trout eggs now exceed the 4-nmol/g thiamine concentration threshold level and meet the definition of viable eggs for restoration efforts (Bronte et al 2008) at most sites; this may partially explain the recent detection of wild recruits.…”

Section: Discussionmentioning

confidence: 99%

Evidence of Wild Juvenile Lake Trout Recruitment in Western Lake Michigan

Hanson

Holey

Treska

et al. 2013

Lake Trout Salvelinus namaycush were extirpated from Lake Michigan by the early 1950s, and as part of an effort to restore naturally reproducing populations, hatchery‐reared fish have been stocked since the early 1960s. Stocked fish are marked with a fin clip to differentiate them from wild, lake‐produced Lake Trout; marking error for the 2007–2010 year‐classes of Lake Trout stocked by federal hatcheries averaged 3.0%. Egg deposition, emergent fry, and wild juvenile Lake Trout have previously been observed, but no sustained wild recruitment has been measured in assessment surveys or in sport and commercial fishery catches. In 2011 and 2012, we caught juvenile Lake Trout in gill‐net and bottom trawl catches that were targeting Bloater Coregonus hoyi in water depths greater than 80 m. Unclipped, wild Lake Trout represented 20% of all Lake Trout caught in a southern offshore region of Lake Michigan. In northwestern Lake Michigan wild recruits represented from 10% to 27% of the 2007–2009 year‐classes, and we recovered a small number of wild Lake Trout from the 2010 year‐class. This is the first evidence for consecutive year‐classes of naturally produced Lake Trout surviving beyond the fry stage in Lake Michigan.Received July 13, 2012; accepted November 26, 2012